Mercury switch



Feb. 24, 1953 2,629,797

J.C.HARDY MERCURY SWITCH Filed Oct. 18, 1951 Fig.

x y l 'i' John 6', Hardy HVVENTDR.

Patentecl Feb. 24, 1953 UNITED STATES PATENT OFFICE MERCURY SWITCH John C. Hardy, Childersburg, Ala.

Application October 18, 1951, Serial No. 251,939

(Cl. G-141) d Claims. l

This invention relates to a mercury switch and particularly to a thermo-responsive switch for use in an alarm circuit.

In the installation of iire alarm switches. it is desirable to have switches that are cheap enough and reliable enough to be placed wherever and however they may be needed to protect the premiscs from fire. Many switches have heretofore been designed for such purpose but they were either too expensive or their operation was too uncertain to warrant their utility. IThe present invention provides a cheap, reliable mercury switch having a base which will screw into a standard base socket so that the switches may be installed wherever they may be needed.

The present switch is constructed with a screw base having an insulating core and a reservoir of mercury contained within the shell. fin expansion tube is connected to the reservo-ir and a plurality of contact wires extend into the expansion tube so that when the mercury expands it will short the Contact wires and maire the circuit. In order to make a self-contained device which may be easily screwed into a standard socket, the contact wires are brought out from the shell and from the usual Contact terminal of the base and extend through the reservoir in insulated relation by such devices as insulating tubes such as glass.

It is an object of this invention to provide an improved mercury switch.

It is a further object of this invention to provide a mercury switch which is self-contained.

It is a primary object of this invention to provide a mercury switch which will screw into a standard socket base.

It is a :further object of this invention to provide a mercury switch having contacts to iit a standard base and terminals extending in inw sulated relation through the reservoir of mercury.

Other objects and many of the attendant advantages of this invention will be apparent from the following detailed description taken in conjunction with the accompanying drawing, in which:

Figure 1 is a sectional elevation through the mercury switch showing the alarm circuit in diagrammatic form;

Figure 2 is a top plan View ci the switch showing the method of connecting to the contact wires; and

Figure 3 is a cross-section through the mercury reservoir taken substantially on the plane indicated by the line 3-3 of Figure 1.

In the exemplary embodiment of the invention, a container l?. of glass or any other insulating material contains a reservoir I2 oi thermal expansion conducting material such as mercury or gallium. An expansion tube I4 has a capillary tube I6 connected tothe reservoir i2 so that on expansion the conducting liquid may extend up through the capillary tube i6. The expansion tube i4 is provided with a bulb-like top I which has a pair of contact wires 2l! and 22 extending through the tcp of the expansion chamber and sealed therein so that the expansion chamber may be substantially evacuated or at least maintained at a relatively low pressure. The top 2t of the expansion tube may, if desired, be a standard press sealing the top to the contact wires 20 and 22. The reservoir lil is assembled into a plug which rits a standard screw base by means of a shell 2li which has a threaded bottom section 2S and an inturned top section 3Q. The bottom section 28 is molded onto an insulating core 32 and a suitable cushioning device 34 is provided between the insulating core 32 and the container l0. Preferably the shell 28 is assembled on the core and the cushioning device 34 is inserted, after which the top edge of the shell 26 is spun over to provide an inturned lip 3i! to retain the reservoir in position in the plug. A pair of hollow tubes 4d and 42, constructed of glass or other similar insulating material, extend through the reservoir l2 and extend upwardly a material distance above the container l. A first conductor 44 is connected to the contact button 493 and extends upwardly through the insulating base or core 32 and upwardly through the hollow tube 4c to extend above the top thereof. The conductor t4 is then conducted to the contact wire 22 to provide one terminal of the switch. A conductor 46 is connected to the shell 25 and extends upwardly through'vthe tube 42 to provide a terminal to the alarm circuit. The other contact wire 2Q extends upwardly to provide the other terminal for the alarm circuit. Preferably the alarm circuit includes a visual and an audible device such as a lamp 50, 52. An alarm circuit 54 extends from the output terminal of the wire 2B through the signallingv devices 50 and 52 to the outer terminal of the conductor 45.

If the signal circuit isof the direct current variety, preferably the terminal 46 is a positive terminal so that the positive terminal is in the make side oi the switch while the negative terminal connects to the shell and to the conductor `lH centrally extending through the switch mechanism. As is usual in such circuits, the shell is preferably grounded.

In the utilization of the thermal expansion switch, the base 28 is screwed into a standard socket, not shown, which is connected to a standard electric source such as an ordinary light circuit or a special direct current circuit. If the latter is used, the terminal 4E is connected to the positive side of the circuit while the shell is grounded or connected to the negative side of the circuit. The negative conductor 46 or the grouuded conductor is extended. through the tube 42 in insulated relation to the reservoir of conducting material within the container I0. The positive side of the line is then connected in the make portion of the expansion chamber so that the expansion of the conducting liquid will bridge the contact wires and complete the circuit 54 to the alarm devices 5D and 52. Obviously, a plurality of switches may be connected in parallel to the same signal devices or each switch may have its own signal device or may be a. plurality oi signal devices either in series or in parallel so that signals may be given at various places by means of the system.

While, for purposes of exempliiication, a particular embodiment of the invention has been shown and described according to the best present understanding thereof, it will be apparent that changes and modifications can be made therein without departing from the true spirit of the invention.

Having described the invention, what is claimed as new is:

1. An alarm switch comprising a screw an insulating core in said base, a conducting shell on said base, a reservoir mounted in said shell, a pair of insulating tubes extending through said reservoir, a conductor extending through each of said tubes, a Contact button on said core, one of said conductors connected to said button, the other of said conductors connected to said shell, an expansion tube connected with said reservoir, a pair of contact wires extending into said expansion tube, one of said nist-mentioned conductors being connected to one of said contact wires, the other of said first-mentioned conductors and the other of said contact Wires forming the output terminals of said switch, a filling oi expansible conducting liquid in said reservoir.

2. An alarm switch comprising a screw base, an insulating core in said base, a conducting shell on said base, a reservoir mounted in said shell, a of insulating tubes extending through said reservoir, a conductor extending through each of said tubes, a contact button on said core, one of said conductors connected to said button, the other of said conductors connected to said shell,

an expansion tube connected with said reservoir, a pair of contact wires extending into said expansion tube, one of said. inst-mentioned con ductors being connected to one of said contact wires, the other of said inst-mentioned conductors and the other of said contact wires forming the output terminals of said switch, a lling of mercury in said reservoir.

3. A thermally actuated switch comprising a circular glass container, a pair of glass tubes extending through said container, a screw base attached to said container, said base including an insulating core, a terminal on said core, a rst conductor connected to said terminal, said first conductor extending through one of said glass tubes, a threaded conducting shell on said core and embracing said container, a second conductor attached to said shell and extending through the other of said glass tubes, a glass expansion tube connected with said container, a pair of contact wires extending into said expansion tube, a quantity of mercury in said container, said container and said expansion tube being otherwise substantially evacuated, said rst conductor being connected to one of said Contact wires, the other contact wire and said second conductor bein?,r the output terminals of said switch.

4. In an alarm system, a thermal switch comprising a reservoir of insulating` mate `ial, a screw base attached to said reservoir, said base including an insulating core, a conducting terminal on said core, a screw/threaded conducting shell on said core, a pair of insulating tubes extending through said reservoir, a rst conductor connected to said terminal and extending through one of said tubes, a second conductor connected to said shell and extending through the other of said tubes, an expansion tube communicating with said reservoir, a pair of Contact wires extending into said expansion tube, said first conductor connected to one of said contact wires, said second conductor and the other contact Wire being the output terminals of said switch, a filling of thermally expansive conducting liquid in said reservoir, said reservoir and said expansion tube being sealed to maintain a low pressure therein.

JOHN C. HARDY.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number 

